Those who are destitute of philosophy may be compared to prisoners in a cave, who are only able to look in one direction because they are bound, and who have a fire behind them and a wall in front. Between them and the wall there is nothing; all that they see are shadows of themselves, and of objects behind them, cast on the wall by the light of the fire. Inevitably they regard these shadows as real, and have no notion of the objects to which they are due. At last, some man succeeds in escaping from the cave to the light of the sun; for the first time he sees real things, and becomes aware that he had hitherto been deceived by shadows. If he is the sort of philosopher who is fit to become a guardian, he will feel it is his duty to those who were formerly his fellow prisoners to go down again into the cave, instruct them as to the truth, and show them the way up. But he will have difficulty in persuading them, because, coming out of the sunlight, he will see shadows less clearly than they do, and will seem to them stupider than before his escape.

Plato (c.428-347 BC) Greek philosopher

The Republic, 7.514

Summ. Bertrand Russell, A History of Western Philosophy, ch. 15 (1946)